The miniaturization of semiconductor devices and the like is advantageous in bringing about an improvement in performance and function (higher-speed operation, lower power consumption, etc.) and a reduction in cost and thus has been accelerated more and more. The lithography technique has been supporting this miniaturization and transfer masks are a key technique along with exposure apparatuses and resist materials.
In recent years, the development of the DRAM half-pitch (hp) 45 nm to 32 nm generations according to the semiconductor device design rule has been progressing. This corresponds to ¼ to ⅙ of a wavelength 193 nm of ArF excimer laser exposure light. Particularly, in the hp45 nm and subsequent generations, only the application of the resolution enhancement technology (RET) such as the conventional phase shift method, oblique illumination method, and pupil filter method and the optical proximity correction (OPC) technique has been becoming insufficient and the hyper-NA technique (immersion lithography) and the double exposure (double patterning) technique have been becoming necessary.
The phase shift method is a technique of giving a predetermined phase difference to exposure light transmitted through a phase shift part, thereby improving the resolution of a transfer pattern using interference of light.
As photomasks improved in resolution by the phase shift method, there are a substrate dug-down type in which a phase shift part is provided by digging down a quartz substrate by etching or the like, and a type in which a phase shift part is provided by patterning a phase shift film formed on a substrate.
As photomasks of the substrate dug-down (carved) type, there are a Levenson-type phase shift mask, an enhancer-type phase shift mask, a chromeless phase shift mask, and so on. As chromeless phase shift masks, there are a type in which a light-shielding layer on lines is completely removed, and a type in which a light-shielding layer on lines is patterned (so-called zebra type). A Levenson-type phase shift mask or a chromeless phase shift mask of the type in which a light-shielding layer in a transfer area is completely removed is also called an alternative phase shifter which is a phase shift mask of the type in which exposure light incident on a phase shift part is transmitted at 100%. An enhancer-type phase shift mask is provided with a light-shielding part, a transmittance control part (phase 360° inversion=0°), and a 180° inversion part formed by digging down a glass. In any type, it is necessary to form a light-shielding part (light-shielding band) in an edge area (peripheral area) along four sides in the photomask (reticle).
As photomasks of the type in which a phase shift part is provided by patterning a phase shift film formed on a substrate, there are a halftone phase shift mask and so on.
As a photomask blank for fabricating such a chromeless phase shift mask described above, there is known a mask blank for a chromeless phase shift mask, having a structure in which, for example, a light-shielding film (having sufficient light-shielding performance (optical density: 3.0 to 4.0) for forming a light-shielding band) comprising a first layer (corresponding to an etching mask film) containing Cr and a second layer mainly composed of MoSi, which are laminated in this order, is formed on an upper surface of a substrate (see JP-A-2007-241136 (Patent Document 1)).
As a photomask blank for fabricating such a halftone phase shift mask described above, there is known a mask blank for a halftone mask, having a stacked structure in which, for example, there is formed, on an upper surface of a phase shift film (MoSi-based film or the like), an etching mask film (Cr-based film or the like) made of a material having etching selectivity to an etching gas (fluorine-based gas or the like) to be used for etching the phase shift film, there is formed, on an upper surface of the etching mask film, a light-shielding film (MoSi-based film or the like) having etching selectivity to the etching mask film and having sufficient light-shielding performance for forming a light-shielding band alone or in a laminated structure with the etching mask film, and further, an antireflection film (Cr-based film or the like) is formed on the light-shielding film (see JP-A-2007-241065 (Patent Document 2)).